helpingme

i have xp version..... my computer started turning it self off i cleaned all dust ect from inside fans ect,, now i got it to come back on but there is a red light on drive that used to flash whilst comp was on now that stays permenatly on, also my screen frezzes and i have to turn computer off and sometimes it wont load up first time you switch it on.... anyone any ideas before i take it to pc world and get ripped off....